Perl's threads did not change between 5.6.1 and 5.8: they were unstable and memory-hungry, now they are same. May be few bugs fixed, but they not ready for use.
Every time I tried to use those, I forced to undo threading after random crashes.
Different folks have different experiences, I guess.
I have found the user level interface to ithreads added in 5.8.0 (that's 'thread' module etc) useful and stable in a number of situations.